4 THE INVOLUNTARY NERVOUS SYSTEM 



myotomes ; the dorso-ventral muscles are found in the cranial 

 segments and form the ocular muscles. This segmentation I 

 have therefore called in both vertebrates and invertebrates the 

 somatic segmentation. 



The striated muscles in the vertebrate, which are derived 

 from the invertebrate appendage muscles, are situated mainly in 

 the cranial region, and form two groups in the adult vertebrate ; 

 (i) the muscles of mastication, which correspond to the muscles 

 of the masticatory appendages in the invertebrate, and (2) the 

 muscles of respiration, which correspond to the muscles of the 

 respiratory appendages. Therefore the segmentation due to the 

 appendages in the invertebrate corresponds to V. Wijhe's ventral 

 segmentation, which I have called splanchnic or visceral. 

 In using the terms somatic and splanchnic to denote these two 

 segmentations instead of the terms mesomeric and branchiomeric, 

 I was dealing throughout only with striated musculature, so that 

 the term somatic denoted a well-defined group of striated body 

 muscles in contradistinction to another well-defined group of 

 striated visceral or splanchnic muscles. It is therefore absolutely 

 erroneous to make use of the term somatic as defined by me, as 

 though it were synonymous with striated, as has been done by 

 Edinger and by Langley and Anderson. 



In Limulus and the Scorpions the region which bears the 

 masticating appendages has been called the prosomatic region, 

 and the region which bears the respiratory appendages the meso- 

 somatic region. The same terms may be used with advantage 

 in talking of the corresponding regions of the vertebrate. 



The more primitive arrangement of the segmental motor 

 nerves in the cranial region to supply the muscles belonging to 

 the somatic and splanchnic segments, corresponding to the 

 somatic and appendage muscles of the invertebrate, is naturally 

 shown also in the origin of the motor fibres from the motor-cell 

 groups in the cranial region. Thus in the prosomatic region 

 (Fig. i) the nucleus masticatorius of the trigeminal together with 

 the series of nuclei, which are described on the so-called descend- 

 ing root of the trigeminal and give origin to the fibres of this 

 so-called root, represent the motor neurons of the splanchnic 

 segmentation, and represent therefore the motor neurons of the 

 muscles of the prosomatic appendages ; they are quite separate 

 from the oculomotor and trochlearis nuclei, which represent the 



